“It's part of our flare system – an area that we are extremely careful in dealing with,” she said. “As always, our first concern is for the health and safety of our employees and the surrounding community.

“Because sour water does contain sulphur, we knew there was a potential for risk, so we called the shelter in place while we confirmed exactly what we were dealing with.”

A CVECO Code 6 calls for full traffic control in designated areas; Sarnia Police blocked all southbound traffic at River Road, Tashmoo Avenue and Highway 40, and a spokesperson for Hull bus lines said school buses heading towards Corunna were held until the all clear was issued around 3:30 p.m.

“We have ... continuous air monitoring in place both in and outside the fenceline to confirm there are no remaining concerns,” said Harradence, noting plant officials were working with the Ministry of the Environment.

“We understand the concerns our neighbours would have as a result of this, and want to ensure we're doing everything we can to resolve this as safely and quickly as we can,” she said.

Aamjiwnaang resident and chair of the Aamjiwnaang Environmental Committee Ada Lockridge said she received phone calls from several concerned residents who reported strong “rotten-egg” odours in their homes, some as early as 11:40 a.m., Friday.

“At this time we believe that the leak started shortly before we discovered it at approximately 1:45 p.m.,” Harradence said in response to the concerns.

The company issued a CVECO information code Thursday evening for odours associated with a separate incident, she said. That code was still in place when the Friday leak occurred.

But the Thursday notification should have been a Code 8, said spokesperson Kristina Zimmer — noting information codes aren’t normally reported to the media.

The other incident was crude leaking from a storage tank on site, Harradence said, and officials issued the code in case there was an odour.

A Code 8 is notification of an internal abnormal occurrence and requires no action from responders.

Information Codes used to be sent out as Information Code 8s, Zimmer said, explaining how the mixup may have occurred.

Even still, the company directly notified St. Clair Township Mayor Steve Arnold, Aamjiwnaang Chief Chris Plain, and Cal Gardener, with the City of Sarnia, Harradence said.

Officials have been monitoring both leaks continuously to make sure there are no health impacts, she said.

“We felt it was better to err on the side of communicating and being cautious.”

Sarnia Mayor Mike Bradley said St. Clair Township is meeting Monday at 10 a.m. to review the incident.